VOLUME 19 (3)/June 1989

No abstract is available for this publication.

The 22 Alpine flysches are of different age. They are classified into greywacke-siltstone, clastic-limestone and tephroidal flysch. Facial zones are coarse, sandy, normal, shaly flysch and subflysch or proximal and distal flysch, as well as deep-sea fans. The sources of flysch are three – exogenic, intra basin and submarine volcano. Flysch comprises rhythmic alternation of normal sediments and resedimentary (clastic) rocks. Sedimentary environments are basin slopes, rises and bottom plains or submarine-volcano slopes, rises and depressions between volcanoes. The floor is of ophiolites, pelagic or shallow-water rocks. Flysch formed upon oceanic transitional and continental crust. The rate of deposition is from 100 to 600 m/m. y. Migration of flysch is from oceans through island arcs and marginal seas to epicontinental troughs. Upwards there is a hiatus (orogeny) but as an exception – transition to post-flysch (molasse). In the sequences flysch is preorogenic, synorogenic or postorogenic. It originates during the mature, senile or final oceanic stage of the Wilson's cycle. The paleogeodynamic environments are 16 in oceans, seas and continents. Models of concrete paleogcodynamic environments have been proposed. In the evolutional stages flysch may be embrional (Anisian), initial (Triassic, Jurassic) and early (Late Jurassic, Early Cretaceous). Early Alpine (Cimmerian-Austrian), middle Laramian (Upper Cretaceous), late Illyrian (Paleogene) and final (Eocece-Miocene) Savian-Stirian (Moldavian). In the Alpine evolution of the Tethyan ocean flysch migrates from north to south.

I. Zagorcev, P. Lilov, S. Moorbath. Results of rubidium-strontium and potassium-argon radiogeochronological studies on metamorphic and igneous rocks in South Bulgaria. Rubidium-strontium whole-rock isochron isotopic studies complemented by potassium-argon studies, permitted the solution of some open problems of the geology of South Bulgaria (South of the Balkanides). Rocks of the Ograždenian Supergroup sufferred an intense Cadomian (550-530 Ma) deforma tional and metamorphic event which is parallelized with the greenschist metamorphism of the Diabase-phyllitoid complex, and with Struma diorite formation. Granitoid magmatism in the high-grade Precambrian basement is referred mainly to two tectonomagmatic cycles: Hercynian (340-240 Ma) and Alpine (Late Cretaceous and Paleogene). The first Hercynian granitoid complex of the South Bulgarian granitoids (340-320 Ma; initial ⁸⁷Sr/⁸⁶Sr ratio about 0.706) is probably related to magma of an initial upper mantle (or lower depleted crust) origination, and subsequent contamination with crustal material followed by differentiation and fractionation. These I-granites have been followed by two main phases of S-granites, their magma being formed by crustal anatexis. Late Cretaceous metamorphic and igneous processes deeply affected the whole Rhodope Massif and the Srednogorie Zone. The rocks of the Rhodopian Supergroup have been reworked by deformational and metamorphic events ca. 100 Ma ago which probably reached to anatexis at deeper levels still not exposed at the present erosion level. During the Early Senonian, magmas of primary upper mantle genesis have been extruded and intruded in the Srednogorie Zone; in the same time, the southern parts of the Rhodope Massif have been intruded by magmas of mixed primary origin, and the central and western parts of the massif - by granitoid magmas of crustal, anatectic origin. The new igneous activization in the Paleogene led to extrusion or intrusion of crustal, anatectic magmas, in the southernmost parts of the Rhodope Massif, of possible mixed origin.

The ophiolite occurence in Samothrace consists of mafic plutonic rocks intruded by W-trending dolerite dikes. The petrographic and geochemical examination suggests tha tthey are gabbros corresponding to the intermediate segment of an ophiolite sequence.
   All rocks studied have tholeitic compositions. In addition the dolerites yield geochemical distribution patterns exhibiting characteristics of island arc tholeites. Our results indicate involvement of a subduction component in the petrogenesis of these rocks. In view o f comparable data reported from similar occurrences elsewhere in the Circum-Rhodope Belt. The probability of a supra-subduction-zone-type tectonic environment is suggested for these ophiolites.

I. Stanev, S. Vesselinov. Vertical zoning of the underground hydrosphere in the Bulgarian part of the Lower Danube artesian basin. The vertical zoning of the underground waters in the southern part of the Lower Danube artesian basin has been studied from the view point of the co-existence of both elisional and intimately related to them infiltration water-bearing systems. The hydrogeological stratification is made on the basis of defined and described marker (peak) surfaces of higher mineralization of the underground waters which enable to divide the underground hydrosphere into four hydrogeological levels - E₁, E₂, E₃ and E₄. The boundaries between the individual levels are marked by three maxima o f higher mineralization of the underground waters which define the marker (peak) surfaces F₁, F₂ and F₃. The two minima of lower mineralization cover the middle parts of the hydrogeological levels E₂ and E₁. The uppermost marker surface F₁ in the hydrogeological level E₁ is followed upwards by a gradual decrease in the mineralization towards the surface which is due to the infiltration influence, and the lowermost marker surface F₃ – by a decrease of mineralization downwards in the hydrogeological level E₄ as a result of dehydration of clays (inversion).
   Particular attention is paid to the character of marker surfaces of higher mineralization which form the hydrogeological structures (positive, negative, inclined). They have a concrete hydrogeological meaning which is directly related to the generation and accumulation of hydrocarbons in view of their prospecting.

V. G. Nikolaev, D. Vass, D. Pogacsas. The Neogene-Quaternary Pannonian basin: a structure of labigenic type. The Neogene-Quaternary sedimentary cover is subdivided into two structural complexes: the lower – Miocene and the upper one, including a part of the Upper Miocene, Pliocene and Quaternary. Narrow relatively elongated structures are typical for the lower complex. The linear zones composed of andesite and rhyolite volcanites developed synchronously. The upper complex forms very gentle isometric structures. Their formation was accompanied by the widespread basaltic volcanism. The maximum thickness of the lower complex deposits is associated with marginal structures of the basin, while that of the upper complex was found in its central part.
   The Miocene (up to the Sarmatian) is characterized by conditions of extension, while the time of formation of the upper complex, predominantly by vertical negative movements.
   The analysis of the structure in the deep-seated part of the Earth's crust suggests that its formation began in the Middle Miocene (the main stage – Upper Miocene/Pliocene) due to the uplift of the mantle diapir. The Pannonian basin, as well as basins of the internal seas of the Mediterranean belt, should be ascribed to a peculiar class of labigenic structures.

No abstract is available for this article.